The present invention relates in general to a sewing machine, and particularly to a cloth feed apparatus for use in a sewing machine.
Generally, there is provided a cloth feed device for feeding a strip of cloth in synchronism with the vertical reciprocal motion of a sewing needle in a sewing machine, which cloth feed device constitutes an indispensable component either in the industrial sewing machines or in the domestic sewing machines.
While the cloth feed device as used in the domestic sewing machine may feed a cloth at a relatively slow feeding speed in accordance with a relatively slow vertical reciprocal motion of the sewing needle, it is often required for the industrial sewing machines to provide a special auxiliary cloth feed arrangement as the vertical sewing motion speed of the needle is extremely high as compared with that in the normal domestic sewing machines. In such special auxiliary cloth feed device, however, it is of such mechanical construction that the rotating motion of the main shaft for driving the sewing needle is once reduced in speed by way of reduction gears, and then converted into a swinging motion by using a crank-chain mechanism, and thus-obtained swing motion is now converted again into an intermittent rotating motion by means of a one-way clutch arrangement so as to rotate the cloth feed roller in such intermittent rotating motion. With such construction, when the up-and-down reciprocal motion of the sewing needle is made at an extremely high speed, the cloth feed roller can not follow properly such intermittent rotating motion at such extremely high speed owing to the inertia of itself and that of the one-way clutch, and then would rather move in a continuous rotating motion, and as a result, such problems have inevitably been brought in practice that the cloth might be fed untimely or improperly while the sewing needle is stitching and still remains staying in the cloth, thus causing the needle to be broken or otherwise in trouble. In addition, there have been caused such troubles that as the durability of the conventional auxiliary cloth feed device to be used at an extremely high speed depends upon the permanence of the one-way clutch at a high speed use, at such a high revolution speed as 3,500 rpm of the main needle driving shaft, the service life of the auxiliary cloth feed device would therefore turn out to be one month or shorter with such occasional troubles as spring broken or the like, that it would likely become relatively heavy in its structural weight, and that as it would inevitably bring a relatively distant gap between the sewing needle and the cloth feed roller, such device cannot serve in a curve tracing in the sewing operation.
In view of the drawbacks as experienced in the conventional auxiliary cloth feed device of mechanical construction as stated hereinbefore, the inventors of the present invention have once proposed an electronic type auxiliary cloth feed device which is adaptable in place of the conventional mechanical type cloth feed device and which can meet such problems inherent to the conventional cloth feed device. However, the electronic type auxiliary cloth feed device proposed by the inventors of the present invention is of such construction that there is produced the electric pulses in accordance with the detection signals developed from the needle position detector, and the stepping motor is driven in stepping rotating motion in accordance with the given electric pulses, when there is once brought a change in the driving speed of the sewing machine main shaft which defines the up-and-down reciprocal motion of the sewing needle, this vertical reciprocal motion of the sewing needles and the cloth feed rate as performed by the stepping motor could hardly be made in proper synchronization with each other any longer, thus disturbing the proper cloth feed so desired. In addition, the pulse generator adapted to generate such electric pulses would generally turn out to be complicated in construction and thus costly in production.
And, according to the conventional techniques, complicated electric circuits are needed for generating pulses suitable to the starting characteristics of the stepping motor. Further, such pulses that are produced in accordance with the starting characteristics have no relation with the revolution speed of the main shaft of the sewing machine so that when the revolution speed of the main shaft is changed the pulses generated in accordance with the starting characteristics become useless.
In consideration of such disadvantages particular to the first proposed arrangement as stated above, the present invention is essentially directed to the provision of an improved electronic type auxiliary cloth feed apparatus which is advantageously adaptable in coping with such drawbacks which are inevitable in the first proposed construction.
It is therefore a primary object of the present invention to provide an improved electronic type auxiliary cloth feed apparatus which can provide a desired cloth feeding effected by means of a rotary mechanism of the apparatus substantially in full synchronism with the vertical reciprocal motion of the sewing needle even in an event that there occasionally occurs a change in the revolution speed of the main driving shaft of the sewing machine, and which is relatively simple in construction.
It is another object of this invention to provide an improved electronic type auxiliary cloth feed apparatus which can effectively reduce a possibility that the sewing needle would be broken or otherwise troubled owing to an occasional asynchronization between the vertical reciprocal motion of the sewing needle and the cloth feed effected by the rotary mechanism of the apparatus.
It is a further object of this invention to provide an improved electronic type auxiliary cloth feed apparatus which can readily be adjusted with its cloth feed rate or speed and amount in accordance with a kind of cloth to be sewn, a sewing or stitching pitch of the sewing needle, or in respect of a temperature and a moisture of the ambient atmosphere, and which can also prevent a slippage puckering or a seam puckering from occurring, whereby there is assured a sewn product of desired quality.